General properties of oscillatory processes occurring in radio engineering, mechanical and other systems, as well as various methods of their study are considered. Much attention is paid to the description of parametric, self-oscillatory, relaxation and other non-linear systems. Mechanisms of oscillation synchronization and stochastic dynamics of simple systems are considered. The study of these oscillatory systems was carried out by known methods of oscillation theory without a detailed presentation and justification of the methods themselves. The most important topics are given tasks for self-solution.